A certain class of open magnetic field topologies is generally suited for stable plasma confinement, namely cusps, however cusp confinement introduces its own challenges. Primary among these is the challenge of minimizing particle loss out through the cusp, but also practical challenges exist related to impurities, high-voltage breakdown, plasma heating, and methods to drive plasma currents.
Minimizing impurity buildup is generally necessary for generating and maintaining high plasma temperatures in low-atomic number plasmas of, for example, deuterium and tritium, and generally impurities form when hot dense plasma impinges on vessel structures such as antennae [Cairns 1991 pg. 42] and support structures [Dolan 1994]. High voltage breakdown can occur on these same elements when high voltages (thousands or millions of volts) across the confinement field are applied for, for example, cusp “plugging” by electrostatic fields [Dolan 1994], or rotation [Abdrashitov 1991].
Another challenge of high-energy plasma physics is plasma heating. Numerous methods exist to heat plasma such as neutral beam injection, electron beam injection, and microwaves. Alternatively radio-frequency resonance, for example ion cyclotron resonance heating (ICRH), comprises effective means for heating plasma to high temperatures such as those required for nuclear fusion and other uses [Cairns 1991].
Finally, it is generally favorable to be able to apply currents to the plasma and generally the means of doing so are related to heating means and thus heating and current drive are closely related [Cairns 1991].
It would be beneficial to those skilled in the art of cusped plasma confinement to have a means of supporting the field coils in such a way as to reduce exposure of the support to hot dense plasma for reducing impurity buildup and improving voltage holding, and that could additionally incorporate heating or current driving schemes.